The invention relates to improvements in staplers and analogous implements. More particularly, the invention relates to improvements in pneumatically operated implements for driving staples, nails and/or other types of fasteners.
It is already known to provide an implement of the above outlined character with a cylinder for a reciprocable piston which can propel a fastener into a workpiece or the like in response to abrupt movement from one toward the other end of the cylinder as a result of admission of pressurized gaseous fluid (normally air) into the one end of the cylinder. It is further known to equip such implements with a main valve having a valving element which overlies the one end of the cylinder and is biased to sealing position by a spring. That (one) side of the valving element which faces away from the one end of the cylinder is normally acted upon by pressurized fluid which assists the spring in maintaining the valving element in sealing position. The flow of fluid in a channel which connects a chamber at the one side of the valving element with a source of pressurized fluid is controlled by a second valve which is remote from the chamber and can be actuated by a trigger to seal the channel from the source of pressurized fluid and to simultaneously or thereafter connect the channel with the atmosphere. This results in a reduction of pressure in the chamber and enables pressurized fluid, which acts against another side of the valving element opposite the one side, to overcome the bias of the spring and to move the valving element to an open or inoperative position. Pressurized fluid is then free to penetrate into the one end of the cylinder and to propel the piston in a direction to drive a fastener into an object or into two or more abutting or overlapping objects.
It is further known to design the source of pressurized fluid in such a way that pressurized fluid is free to penetrate into the one end of the cylinder all the way around the one end, as soon as the valving element of the main valve is caused to assume its inoperative position. This entails a more uniform application of fluid pressure to each portion of the piston and more predictable propulsion of the piston toward the other end of the cylinder. Moreover, such mode of regulating the admission of pressurized fluid into the one end of the cylinder is intended to promote rapid acceleration of the piston and to thus increase the force with which the piston propels a fastener into one or more objects when it approaches or reaches the end of the working stroke. The arrangement is normally such that the valving element of the main valve constitutes a relatively large lid which overlies the one end of the cylinder and can perform strokes in the range of several millimeters.
A drawback of the just described conventional implement is that the path for evacuation of fluid from the chamber at the one side of the valving element of the main valve to the locus of discharge into the atmosphere is very long and normally includes numerous arcuate portions. All this contributes to a pronounced resistance to the flow of fluid from the chamber into the atmosphere and prevents pressurized fluid in the source from rapidly moving the valving element to its inoperative position. Therefore, the initial acceleration of the piston in response to movement of the valving element from the sealing position is unsatisfactory and the force which the piston applies to a fastener at the end of its stroke is often insufficient.
The aforementioned spring opposes the movement of the valving element to the inoperative position. Nevertheless, such spring is necessary and desirable because it reduces the likelihood of injury to a user of the implement. Thus, the spring ensures that the valving element of the main valve assumes its operative position when the implement is not in use as well as when the source of pressurized fluid in the housing of the implement is connected to an outside source of pressurized fluid, particularly by way of a hose or another suitable conduit.
Another drawback of conventional implements is that the useful life of their springs is rather short. This is due to repeated stressing of the springs and to repeated dissipation of energy. A broken spring is likely to cause injury and/or partial or complete destruction of adjacent parts of the implement.